1. Field of the Invention
The present invention relates generally to heating, ventilating and air conditioning (HVAC) systems of vehicles and, more specifically, to a temperature and humidity sensor for a HVAC system in a vehicle.
2. Description of the Related Art
It is known that a fundamental goal of a HVAC system for a vehicle is to detect and avoid windshield/window fogging conditions. In an attempt to measure and control the many variables that affect fogging, modern HVAC systems have many sensors and control actuators. A typical HVAC system might have a temperature sensor inside an occupant compartment or cabin of the vehicle, one measuring ambient temperature outside and others measuring various temperatures of the HVAC system internal workings. The occupant may have some input to the HVAC system via a set point or other adjustment. Additional sensors measuring sun heating load, humidity, etc. might be available to the HVAC system. The set of actuators might include a variable speed blower, some means for varying air temperaturexe2x80x94including cooling and thereby extracting moisture from the air, ducting and doors to control the direction of air flow and the ratio of fresh intake air to recirculated air.
It is known how to provide a method and control system for controlling the HVAC system to prevent fogging. Such a method and control system is disclosed in U.S. Pat. No. 5,516,041 to Davis, Jr. et. al., the disclosure of which is hereby incorporated by reference. In this patent, the method and control system uses fuzzy logic to prevent fogging. The control system responds to signals generated by various climate control sensors including a humidity sensor to produce a desired vehicle air temperature and airflow to detect and avoid incipient windshield/window fog conditions. Fuzzy logic and calculations are performed based on fuzzy rules and membership functions to provide nonlinear compensation. The fog boundary is mapped out empirically.
Current electronic air temperature controllers (EATCs) do not have the capability to determine if the windshield is fogging or about to fog. Therefore, it is desirable to provide a temperature and humidity sensor assembly to allow an EATC to determine when fogging will occur and take appropriate climate control system actions to avoid windshield fogging or misting. It is also desirable to provide a temperature and humidity sensor assembly supplied with aspirated cabin air to allow absolute cabin humidity to be monitored. Therefore, there is a need in the art to provide a temperature and humidity sensor assembly that accomplishes these desires.
Accordingly, the present invention is a temperature and humidity sensor assembly for a heating, ventilation and air conditioning (HVAC) system of a vehicle. The temperature and humidity sensor assembly includes a housing for connection to the HVAC system. The temperature and humidity sensor also includes a humidity sensor disposed within the housing and a temperature sensor disposed within the housing. The temperature and humidity sensor further includes a circuit board disposed in the housing and electrically connected to the humidity sensor and the temperature sensor and for connection to an electronic controller to control the HVAC system.
One advantage of the present invention is that a temperature and humidity sensor assembly is provided to allow an EATC to determine when fogging will occur and take action to prevent it. Another advantage of the present invention is that the temperature and humidity sensor is supplied with aspirated cabin air to allow absolute cabin humidity to be monitored. Yet another advantage of the present invention is that the temperature and humidity sensor assembly has a capacitive humidity sensor packaged in combination with an incar temperature thermistor that has aspirated air from the cabin of the vehicle drawn across it. Still another advantage of the present invention is that the temperature and humidity sensor assembly has an output that is read by an EATC and is used by various strategies to improve comfort, reduce fogging and improve fuel economy of the vehicle. A further advantage of the present invention is that the temperature and humidity sensor assembly has two sensors sampling the same parcel of air to allow the HVAC system to infer absolute humidity and dew point.
Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.